‖n.; pl. Aciculæ [ L., a small needle, dimin. of acus needle. ] (Nat. Hist.) One of the needlelike or bristlelike spines or prickles of some animals and plants; also, a needlelike crystal. [ 1913 Webster ]

a. Needle-shaped; slender like a needle or bristle, as some leaves or crystals; also, having sharp points like needles. [ 1913 Webster ]

A*cic"u*lar*ly, adv.. [1913 Webster]

{ a. (Nat. Hist.) (a) Furnished with aciculæ. (b) Acicular. (c) Marked with fine irregular streaks as if scratched by a needle. Lindley. [ 1913 Webster ]

a. [ L. acicula needle + -form. ] Needle-shaped; acicular. [ 1913 Webster ]

n. (Min.) Needle ore. Brande & C. [ 1913 Webster ]

n. 1. A sour substance. [ 1913 Webster ]

2. (Chem.) One of a class of compounds, generally but not always distinguished by their sour taste, solubility in water, and reddening of vegetable blue or violet colors. They are also characterized by the power of destroying the distinctive properties of alkalies or bases, combining with them to form salts, at the same time losing their own peculiar properties. They all contain hydrogen, united with a more negative element or radical, either alone, or more generally with oxygen, and take their names from this negative element or radical. Those which contain no oxygen are sometimes called hydracids in distinction from the others which are called oxygen acids or oxacids. [ 1913 Webster ]

☞ In certain cases, sulphur, selenium, or tellurium may take the place of oxygen, and the corresponding compounds are called respectively sulphur acids or sulphacids, selenium acids, or tellurium acids. When the hydrogen of an acid is replaced by a positive element or radical, a salt is formed, and hence acids are sometimes named as salts of hydrogen; as hydrogen nitrate for nitric acid, hydrogen sulphate for sulphuric acid, etc. In the old chemistry the name acid was applied to the oxides of the negative or nonmetallic elements, now sometimes called anhydrides. [ 1913 Webster ]

a. [ L. acidus sour, fr. the root ak to be sharp: cf. F. acide. Cf. Acute. ] 1. Sour, sharp, or biting to the taste; tart; having the taste of vinegar: as, acid fruits or liquors. Also fig.: Sour-tempered. [ 1913 Webster ]

He was stern and his face as acid as ever. A. Trollope. [ 1913 Webster ]

2. Of or pertaining to an acid; as, acid reaction. [ 1913 Webster ]

adj. 1. yielding an acid in aqueous solution [ WordNet 1.5 ]

a. (Min.) 1. Containing a high percentage of silica; -- opposed to basic. [ 1913 Webster ]

2. of or relating to acid; having the character of an acid, as an acidic solution. [ PJC ]

a. [ L. acidus sour + -ferous. ] Containing or yielding an acid. [ 1913 Webster ]